#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=2e5;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL sz[maxn];
vector<LL>g[maxn];
LL ans=0;
void dfs(LL u,LL fa){
     sz[u]=1;
     for(int i=0;i<g[u].size();i++){
        LL v=g[u][i];
        if(v==fa) continue;
        dfs(v,u);
        if(sz[v]%2==0) ans++;
        else sz[u]+=sz[v];
     }
}
int main(void){
   	cin.tie(0);std::ios::sync_with_stdio(false);
    LL n;cin>>n;
    for(LL i=1;i<n;i++){
        LL x,y;cin>>x>>y;
        g[x].push_back(y);
        g[y].push_back(x);
    }
    dfs(1,-1);
    if(n&1) cout<<"-1"<<endl;
    else cout<<ans<<endl;
    return 0;
}
